The present invention relates to a device for preventing collision risks between aircraft operating under VFR (Visual Flight Rules).
The invention is adapted to the piloting rules used by VFR pilots, the basic principle of which is: see and be seen. In effect, the reason most commonly found in reporting of accidents involving collision is the inability of the pilot to see the other aircraft in time. It is therefore desirable to improve the safety of all aircraft flying under visual flight rules without running the risk of changing the rules, customs and habits of pilots who fly under VFR.
To this end, account needs to be taken of the specific aeronautical constraints on light VFR aviation. Gliders in particular are subjected to the most stringent constraints because:
available energy is limited to the use of one additional 12 V/6 A.h battery;
the space available is in the order of a few cubic decimeters;
the maximum mass per square centimeter and the total mass are restricted due to the need to comply with certification constraints;
the addition of external antennas to the fuselage would be detrimental, as would any change in the aerodynamics of the craft. A system that would satisfy these constraints will generally be suitable to all the other categories of aircraft flying under VFR, in particular light aircraft, helicopters, ULM . . .
A number of anti-collision devices currently exist, co-operative or autonomous, which are used in aeronautical applications.
Two categories of known autonomous devices may be cited:
1) Passive devices, which are generally optical and of the infrared sensor type, offer high performance in military applications where the targets have adapted infrared signatures.
2) Active devices, of the airborne radar type, require transmission and reception of a radar wave. The bandwidth of the signal determines the distance resolution performance. Other criteria, such as wavelength, determine the size of transmission and reception antennas.
Five categories may be cited among the co-operative devices:
1) Some devices seek to increase the aircraft visibility (anti-collision lights, colored stripes painted or adhered to gliders, . . . ). These devices generally depend on the type of aircraft on which they are used. They do not significantly increase the pilot""s ability to look in the right place in good time.
2) Other devices are designed to optically detect the flashing anti-collision lights of aircraft. However, these lights are not provided on all VFR aircraft. Secondly, the range of these devices is limited (approximately 1 km), which seems inadequate given the typical speeds at which light aircraft travel and the average reaction times.
3) Systems of the xe2x80x9cTCASxe2x80x9d type (Traffic alert and Collision Avoidance Systems) require a substantial source of energy and the installation of two sets of transmitting and receiving antenna respectively on the upper and lower parts of the aircraft. They operate as a real on-board secondary radar. They are only able to detect aircraft fitted with operating transponders, which is not usually the case with VFR aircraft. Some of these systems use trajectographic algorithms to suggest avoidance maneuvers to the pilots. TCAS II, in particular, became compulsory in the USA in 1993 for all craft having more than thirty seats.
4) Variants of TCAS require the support of secondary air control radar to listen to the transponders of neighboring aircraft when interrogated. This secondary radar support is not available all over the world and makes the system dependent on ground installations.
5) Radio-electric devices of the beacon type may incorporate a position-detecting means, a data transmitter and receiver, a unit for computing potential conflicts and a display device for the pilot. An example of such a device is described in U.S. Pat. No. 4,835,537. Like the TCAS, these devices do not seem particularly well suited to VFR flight conditions since they require the use of display screens on which relatively complex information is presented, some of which relates to aircraft presenting virtually no risk of collision. The pilot""s attention is somewhat distracted by the instrument, which goes against the very principle of the visual flight rules.
Therefore, no collision prevention device is available today which is particularly adapted to cover specific aspects inherent in the safety of all aircraft types flying under VFR rules. In particular, there is no device capable of taking account of complex trajectories such as those of gliders moving in ascending spirals, which cause a considerable number of accidents.
The purpose of the invention is to propose anti-collision devices of the co-operative type which are especially well suited to VFR conditions.
Accordingly, the invention proposes a device to assist piloting under visual flight rules, to be installed on board an aircraft and comprising:
measuring means for estimating at least the instantaneous position and velocity vector of the aircraft;
a radio transceiver for broadcasting co-operation messages containing parameters representing at least the estimated instantaneous position and velocity vector of the aircraft and for receiving similar co-operation messages broadcast by other aircraft;
means for analyzing the co-operation messages received by the radio transceiver and data output by the measuring means, to identify potential risks of collision with other aircraft; and
a man-machine interface to alert the aircraft pilot to potential risks of collision identified by the analysis means.
According to the invention, the analysis means are arranged to perform the following operations at successive instants of analysis:
sub-dividing an analysis period, commencing at the current instant of analysis, into a series of consecutive time intervals;
for each of said time intervals, determining a protected volume on the basis of different possible future positions of the aircraft derived from the data output by the measuring means;
extrapolating the trajectory of each other aircraft from which a co-operation message is received, on the basis of the parameters contained in said co-operation message, so as to estimate possible positions of said other aircraft in the time intervals of the series; and
if a condition is satisfied whereby an estimated possible position of another aircraft in one of said time intervals in the series is located within the protected volume determined for said time intervals, controlling the man-machine interface to issue the pilot with a signaling message indicating the direction in which said other aircraft is located at the current instant of analysis.
Being co-operative in nature, the device is common to all aircraft which fly under VFR rules, including gliders in particular, and is operated a priori all over the world without the constraints inherent in any other control mechanisms or dependent on ground-based installations.
The device can operate to an accuracy that will enable compliance with the average reaction time of a VFR pilot. According to some studies, this time has been estimated at 12.5 seconds between the instant at which the pilot sees the other aircraft and the instant at which he avoids it, including sighting the object (0.1 s), recognizing it (1 s), realization of the certainty of collision (5 s), the decision to turn (4 s), the muscular reaction (0.4 s) and the average response time of a light aircraft or glider (2 s).
The nature and operation of the device do not require to change the rules, customs and habits of pilots flying under VFR, or impose additional workload on them.
Preferably, the signaling message also indicates the time remaining until the first of the time intervals in the analysis period for which said condition is fulfilled. This will enable the pilot to assess how urgently he needs to act.
In order to facilitate visual location of the other aircraft, the signaling messages advantageously include an indication of an apparent size of the other aircraft, determined on the basis of real size indications included in the co-operation messages and of the distance between the two aircraft.
Preferably, the man-machine interface comprises means for issuing signaling messages in the form of voice messages. This being the case, the device does not divert the visual attention of the pilot towards the interior of the cockpit, unlike most anti-collision systems designed for light aircraft, which use a display screen to provide the pilot with a graphical presentation of the traffic and/or potentially conflicting aircraft nearby. The structure of the signaling voice message may be in accordance with a specific phraseology, comparable with conventional radio telephone messages, e.g.: xe2x80x9cTraffic, 15 seconds, 11 o""clock, 10xc2x0, size 2xe2x80x9d. Thus, a pilot used to receiving such information messages will be able to locate the aircraft posing a potential danger very rapidly. He will then be able to take the right decisions to avoid collision in view of the situation.
It will be left to the pilot to assess and choose the best avoidance maneuver, on the basis of the information supplied by the device and in compliance with the VFR rules which he must apply. Accordingly, the principle of the visual flight rules based on observing the surrounding space for 90% of the time will be satisfied.
The nature of the device and the algorithm used to process the available data enable a good adaptation to the different categories of aircraft in question, taking account of their speed, the way they move, their mean distribution density, the available space and the available on-board energy sources.
In a preferred embodiment of the device, the measuring means are arranged to estimate the instantaneous turning radius of the aircraft in a horizontal plane, on which the possible future positions of the aircraft depend, which the analysis means use as a basis for determining the protected volumes. By thus adapting the relevant protected volumes to the instantaneous turning radius of the aircraft, the effective risks of collision are better taken account of.
The duration of the analysis period is advantageously selected as an increasing function of the instantaneous turning radius if the latter is estimated by the measuring means, for example as the minimum between a reference period (or maximum warning time) and a time proportional to the ratio between the instantaneous turning radius estimated by the measuring means and the modulus of the projection on the horizontal plane of the instantaneous velocity vector estimated by the measuring means.
This limits the amount of information presented to the pilot, who is negotiating the turn, so as not to distract his attention, by avoiding issuing alerts to aircraft which are too far away to pose a real risk of collision given the instantaneous velocity and turning radius. This advantage is particularly useful in the case of gliders which have a small turning radius when in an ascending spiral and are often surrounded by other gliders which should be signalled in due course.
The device is preferably adjustable by the pilot regarding the maximum collision risk warning time. This will give him additional comfort corresponding to the reaction time which he prefers to allow himself depending on his personal capabilities, the average quantity of information which he would like to be delivered and the current flight phase (take-off, cruise, approach . . . ).
The nature of the device enables a relatively simple implementation and inexpensive manufacture. It may therefore be fitted systematically by small aircraft owners, unlike some of the other, relatively expensive devices. Widespread use of this device can thus be achieved, a condition crucial to enhancing flight safety.